Wastewater comes in many forms and often needs to be treated by separating contaminants from water carrying the contaminants so that contaminants may be disposed of or further processed and contaminant-free water may be returned to other useful purposes or to the environment. Of course, such treatment is not limited to water, and as used herein, the term wastewater and water refers not only to water but to any liquid from which contaminants, such as dissolved salts, dissolved and/or suspended solids, volatile organic compounds, and so forth, need to be removed for various reasons.
A common way of separating the water from the contaminants is to evaporate some or all of the water from a stream or body of wastewater such that the water is separated in gaseous form from the contaminants. There are of course numerous ways to evaporate water from a standing body of wastewater, including the use of evaporation ponds, boiling, agitation of the wastewater, and so forth. Unfortunately, these methods often either take too long to evaporate the water, for example, when just sitting in an open containment pond, or they can require large amounts of applied energy, such as when fuel or electrical power is applied to cause boiling.
A leachate evaporation system 10 designed to avoid some of the drawbacks above is shown in FIG. 1. In this system, leachate from a landfill is injected at high pressure into a flowing stream of heated waste gas from a flare stack (not shown) as the gas is drawn under negative pressure created by induced draft fan 30 through a mixing chamber 12 of a wetted wall adjustable throat venturi evaporator. In the venturi evaporator, the heated waste gas and the leachate are drawn through a venturi 14, which has a restricted throat having a smaller cross-sectional area than the adjacent mixing chamber 12. The venturi 14 mixes and evaporates at least some of the water from the leachate into gaseous form. The mixed concentrated leachate and gases are then drawn together through a cyclonic entrainment separator assembly 16, which separates evaporated water and waste gas from unevaporated leachate and solids, exhausts the evaporated water and waste gas to the atmosphere, and collects the leachate and solids for further processing and/or disposal.
The cyclonic separator assembly 16 is in the form of a vertically oriented cylindrical vessel with four distinct regions: a lower separator chamber 18 into which the mixed leachate and gases are drawn, a sludge settling tank 20 disposed below the lower separator chamber, an upper separator chamber 22 immediately above the lower separator chamber, and an exhaust stack 24 exiting from above the upper separator chamber. The upper and lower separator chambers are separated by an inverted frustoconical divider 26 with a small central opening at the bottom thereof to allow separated leachate and solids to drip downwardly from the upper separator chamber to the lower separator chamber through the opening. The inverted frustoconical divider 26 also substantially obstructs flow of gases from the lower chamber upwardly into the upper chamber. Thus, a U-shape duct 28 with a first opening into the lower chamber and a second opening into the upper chamber allows the gases to flow from the lower chamber to the upper chamber around the inverted frustoconical divider. A fan 30 is disposed in the duct 28 to draw gases from the lower separator chamber 18 and push the gases into the upper separator chamber 22. An outlet from the venturi 14 and the ends of the U-shaped duct 28 each preferably opens through the side wall of the cyclonic separator in a tangential direction so as to promote cyclonic, i.e., spiral, flow of gases and suspended liquids and solids upwardly from the bottom of the lower separator portion up toward the top of the separator assembly.
The sludge settling tank 20 is partly separated from the lower chamber by a horizontal plate 32 that partially covers the sludge settling tank. Further a first vertical baffle 34 extends partway down from the horizontal plate toward the bottom of the sludge settling tank, and a second vertical baffle 36 laterally offset from the first baffle extends upwardly from the bottom of the sludge settling tank, thereby providing a tortuous up and down path for the leachate to pass from the lower portion of the separator to a recirculation line 38 that connects the sludge settling tank with a leachate delivery line 40. The sludge settling tank is effectively the very bottom end of the cylindrical vessel and has the same diameter as the lower separator chamber.
In use, the leachate and heated waste gas are brought together in the mixing chamber 12 immediately upstream of a venturi 14. As the heated waste gas and leachate move through the venturi, the increased velocity and corresponding drop in static pressure caused by the venturi causes the leachate to thoroughly mix with the heated gas and accelerates evaporation of water from the leachate into a gaseous state. Thereafter the mixed leachate and gases are drawn into the lower separator chamber of the cyclonic separator, and the cyclonic motion of the gas, leachate, and solids upwardly and around the cyclonic separator causes solids and suspended water droplets to fall out downwardly towards the sludge settling tank or collect on the peripheral wall of the vessel, while the gaseous water and waste gas move upwardly and are drawn by the fan through the U-shape duct into the upper separator chamber. In the upper separator chamber, further separation occurs due to continued cyclonic motion of the gases, and the gaseous water and waste gas are ejected through the exhaust opening. Any fluids and solids separated from the gases in the upper separator chamber fall by gravity down through the opening in the inverted frustoconical divider and drop to the sludge settling tank. In the sludge settling tank suspended solids settle towards the bottom of the tank while liquid leachate flows up and over the second baffle and out of the settling tank through the recirculation pipe back into the leachate supply line, to be injected again into the leachate evaporator system. Accumulated solids in the form of sludge may be removed through a sludge removal port near the bottom of the sludge settling tank.
There are several limitations to the design of this evaporator system. A first limitation is that the design elements required for optimizing the functioning of the cyclonic separator and the settling tank are not necessarily compatible in terms of integrating them into a single vertical cylindrical body. Specifically the diameters of the cyclonic separator chambers, the settling tank, and the exhaust stack have significant impacts on the performance of each, and the design parameters for each are independent in terms of what works best. Thus where high velocity of gases is desirable in the cyclonic separator portions in order to both separate the solids and liquids from the gases and also to prevent build up of scale and/or sludge inside the cyclonic separator, in the sludge settling tank, low velocity and quiescence are more desirable in order to promote settling and separation of solids from the liquid. Further, high rates of recirculation flow of liquids from the sludge settling tank necessary to adequately feed the mixing chamber in order to prevent troublesome spray drying of suspended or dissolved solids that would stick to and build up on the walls of equipment downstream are at odds with the need for quiescence to promote the settling of the solids from the liquids.
Another limitation is the relatively small opening in the inverted frustoconical baffle that separates the upper separator chamber from the lower separator chamber. This opening needs to be small enough to prevent significant recirculation of gas from the upper portion to the lower portion around the fan; however, the relatively small opening can be prone to blockage due to build of precipitated solids.
A further limitation is the use of relatively high pressure nozzles to spray leachate into the mixing chamber at elevated pressures, such as in the range of twenty to fifty psig, which may be highly susceptible to fouling and/or blockage by buildup of dried solids in the leachate. The risk of this occurring would increase as the concentration of leachate from the sludge settling tank 20 increases in the recirculation system, which imposes limits on the degree of concentration that can be attained and negatively impacts on the reason why evaporative treatment was chosen in the first place.
Further the entire system suffers from a maintenance stand point by being difficult to access and clean any accumulated solids, sludge, and/or scale from the interior of the cyclonic separator and the evaporator system as a whole.
Therefore the inventors of the concentrator systems disclosed herein have attempted to overcome or improve on one or more of these limitations of this evaporator system.